Changes coming into effect from Monday will see families with one parent earning more than £50,000 lose part of their child benefit.

It will be fully withdrawn where one parent earns above £60,000.

'Fundamentally fair'

Analysis

By Paul LewisPresenter, Money Box

If you or your partner get child benefit and either of you has an income of above £50,000 a year you may have to pay more tax from Monday.

The income that counts is confusingly called 'net-adjusted income'. In fact, it is your gross income before tax from all sources but minus pension contributions, child care vouchers, and gift aid donations.

If you live as a couple it is the higher income that is counted not your joint income.

If that income is more than £50,000, the person who earns it will have to pay a new tax called 'high income child benefit charge'. It will be collected through self-assessment and you must register with HMRC by 7 October.

If that income is £50,000 to £60,000, the charge will be less than the child benefit received on a sliding scale - at £55,000 it will be 50% of the child benefit received.

If that income is £60,000 or more, the charge will equal the child benefit received. In other words, one partner will get the child benefit but the higher earning partner will pay it all back in the new tax.

Defending the policy, Mr Cameron said: "I'm not saying those people are rich, but I think it is right that they make a contribution.

"This will raise £2bn a year. If we don't raise that £2bn from that group of people - the better off 15% in the country - we would have to find someone else to take it from."

He added: "I think people see it as fundamentally fair that if there is someone in the household earning over £60,000 you don't get child benefit... I think it is the right approach."

Asked about government plans to cap working age benefits at 1% - including the rise in the pay of public sector workers, out-of-work benefits, and tax credits - Mr Cameron said "those are all in my view absolutely right decisions".

"We need to control public sector pay... we need to limit the growth of welfare payments overall - and that must include the tax credit system, and for those out of work it's right that their incomes aren't going up faster than people in work."

The prime minister also insisted the government was going "full steam ahead" with a packed agenda in the second half of its term.

In the wide-ranging interview, Mr Cameron made a number of major points, including: